JP2001318042A - Two-dimensional distribution measuring device of surface tension and viscosity coefficient of liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a two-dimensional distribution of the surface tension and the viscosity coefficient of liquid at high speed by detecting the two-dimensional distribution of Brillouin scattering caused by ripplon of the liquid sample surface. SOLUTION: A light source 21, a dividing means BS for bisecting light emitted therefrom, an incident light deflection means M3 for facing one divided incident light 2 toward the liquid surface 1 at a prescribed incident angle, a reference light deflection means M4 for facing the other reference light 5' toward the same position P on the liquid surface 1 at a different prescribed incident angle, a means M5 for allowing mirror-reflected reference light 5 from the liquid surface 1 and scattered light 4 scattered in the direction to enter a photo detector 22, and the photo detector 22 are fixed on a common substrate 20. The substrate 20 is mounted on a two-dimensional scanning means 13 for mechanically executing two-dimensional scanning within the horizontal plane on a sample stand 11 for loading a sample liquid 30. A light heterodyne signal from the photo detector 22 is inputted into a Fourier transform means 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a two-dimensional distribution of surface tension and viscosity of a liquid, and more particularly to an apparatus for measuring two-dimensional distribution of surface tension and viscosity using a repron scan technique.

[0002]

2. Description of the Related Art Thermophysical properties such as surface tension, viscosity or thermal conductivity are known.
Rties) has conventionally been measured by obtaining information at one point of the liquid. For example, the surface tension of a high-temperature melt such as molten silicon has been measured by dropping a molten sample on a ceramic plate and measuring the shape of the sample in a stationary state (static drop method).

On the other hand, as a technique for measuring these thermophysical properties remotely without contact, a method utilizing Brillouin scattering by a ripron is known.

[0004] That is, even if the surface of the liquid is macroscopically uniform, microscopically, thermal fluctuations are always present, so that the surface of the liquid is not a perfect plane but is slightly deformed. . This surface deformation can be considered as a superposition of thermally excited random surface waves. Each wave has a wavelength of about 100 μm and an amplitude of about 1 nm, and is called a ripron as a ripple quantum. Have been. FIG.
As shown in (a), when the laser light is irradiated on the liquid surface 1 as the incident light 2, scattered light 4 is observed around a normal specular reflection component 3. The scattered light 4 contains information on the frequency and attenuation rate of the ripron, and it is known that it is possible to obtain the surface tension and viscosity of the liquid by analyzing this and using the dispersion relational expression. Have been.

Conventionally, an apparatus for determining the surface tension and viscosity of a liquid sample by determining the frequency distribution of the scattered light emitted to the reflection side by the ripron by the optical heterodyne method, and determining the center frequency, half width and wavenumber of the ripron. (Transactions of the Japan Society of Mechanical Engineers (B) 59-56)
No. 0 (1993-4) pp. 185-191). In this case, as the reference light for heterodyne detection, the diffracted light diffracted from the incident light by the diffraction grating is used, and the diffracted light is collected again at the incident light position on the liquid surface by the lens so that the wave number of the replon is obtained. Is easy to seek.

Further, the frequency distribution of the scattered light emitted to the transmission side of the transparent sample by the replon is determined by the optical heterodyne method, and the center frequency, half width and wave number of the ripron are determined, thereby similarly obtaining the surface tension of the transparent liquid sample. And a device for determining the viscosity have been proposed (Rev. Sci.
Instrum. Vol. 62, No. 5, pp. 11
92-1195; Jpn. J. Appl. Phys. V
ol. 36 (1997), p. 2951-295
4). In these cases, light split from incident light is used as reference light for heterodyne detection, and the reference light is again adjusted to the incident light position on the liquid surface by a reflecting mirror.

[0007]

In both the above-mentioned conventionally proposed static droplet method and the method utilizing Brillouin scattering by the ripron, basically, the surface of the liquid surface is reduced to one.
It is a measurement of points (or the average value of the whole), and it has been said that no two-dimensional distribution measurement of thermophysical properties such as surface tension and viscosity has been performed so far, and that there was no need for it. Not too much.

However, in high value-added manufacturing, as represented by the advancement of silicon single crystal manufacturing, there are cases where precise process control cannot be performed only by temperature and pressure. For example, since the surface tension varies greatly not only with the temperature but also with the composition, in order to monitor the non-uniformity of the composition or, conversely, in order to positively add the non-uniformity, the surface tension, viscosity, etc. It is necessary to measure the two-dimensional distribution of thermophysical property values at high speed.

The present invention has been made in view of such a situation of the prior art, and an object of the present invention is to detect the two-dimensional distribution of Brillouin scattering due to riprons on the surface of a liquid sample to thereby reduce the surface tension of the liquid. An object of the present invention is to provide a device capable of measuring a two-dimensional distribution of viscosity at high speed.

[0010]

The two-dimensional distribution measuring device for the surface tension and the viscosity of the liquid according to the present invention, which achieves the above object, comprises:
The light having a predetermined wavelength is divided into two parts, one of which is incident light and the other is used as reference light, and is incident on the same position on the liquid surface at mutually different incident angles. The reference light is specularly reflected from the liquid surface and scattered in that direction. The optical heterodyne signal is detected by interfering with the scattered light of the incident light, and the frequency and the attenuation rate of the replon on the liquid surface are obtained from the power spectrum obtained by Fourier transforming the optical heterodyne signal. In a device for measuring the surface number and viscosity of the liquid from the angle of incidence and the scattering angle of the scattered light and the wave number of the incident light, the wave number of the ripron is obtained, and the frequency and the attenuation rate of the obtained ripron and the wave number of the incident light are obtained. A light source that emits the light of the predetermined wavelength, a light beam splitting unit that divides the light of the predetermined wavelength into two, and an incident light deflecting unit that directs one of the divided incident lights toward the liquid surface at a predetermined incident angle,
Reference light deflecting means for directing the other divided reference light to the same position on the liquid surface at a predetermined incident angle different from the incident angle of the incident light, and the reference light mirror-reflected from the liquid surface and scattered in the direction. The means for selectively causing the scattered light of the incident light to enter the photodetector, and the photodetector are fixed on a common substrate, and the substrate is located in a horizontal plane on a sample stage on which the sample liquid is placed. Wherein the optical heterodyne signal from the photodetector is input to a Fourier transforming means.

In this case, it is desirable that the angles of the incident light deflecting means and the reference light deflecting means can be adjusted.

The measuring apparatus of the present invention is suitable for being applied to a liquid opaque to incident light as a sample liquid, for example, a high-temperature melt.

In the apparatus for measuring the two-dimensional distribution of the surface tension and the viscosity of a liquid according to the present invention, as described above, a light source for emitting light of a predetermined wavelength, a beam splitting means for dividing the light of the predetermined wavelength into two, Incident light deflecting means for directing one of the divided incident lights toward the liquid surface at a predetermined incident angle, and the other divided reference light at the same position on the liquid surface at a predetermined incident angle different from the incident angle of the incident light. A reference light deflecting unit for directing, a unit for selectively causing the reference light specularly reflected from the liquid surface and the scattered light of the incident light scattered in that direction to the photodetector, and a photodetector common substrate The substrate is attached to a two-dimensional scanning unit that mechanically performs two-dimensional scanning in a horizontal plane on a sample stage on which a sample liquid is placed, and an optical heterodyne signal from a photodetector is provided. Configured to be input to Fourier transform means Since the two-dimensional distribution measurement of surface tension and viscosity of the sample liquid also did the need also attempted without becomes possible by a simple device lightweight ever. The apparatus of the present invention is, for example, installed in an actual Czochralski method furnace to measure the surface tension distribution of an opaque and high-temperature melt such as molten silicon in the Czochralski method at the stage of crystal growth. And can contribute to obtaining uniform crystals.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an apparatus for measuring a two-dimensional distribution of surface tension and viscosity of a liquid according to the present invention will be described.

Before describing the embodiments, the measurement principle of the present invention will be described. As shown in FIG. 2A, when the liquid surface 1 is irradiated with a laser beam as the incident light 2, a normal specular reflection component 3
Scattered light 4 is observed around. As described above, the scattered light 4 contains information on the frequency and the attenuation rate of the ripron, and the scattered light 4 is analyzed to obtain the surface tension and the viscosity of the liquid by using the dispersion relational expression of the surface wave. It is possible.

If the traveling direction of the ripron is taken on the x-axis, the displacement ζ of the liquid surface of the ripron can be expressed as follows, where t is the time.

Ζ (x, t) = ζ ₀ cos (kx) · exp (αt) (1) where ζ ₀ is the initial amplitude, k is the wave number of the repron, and α is represented by the following equation. Complex angular frequency.

Α = −iω ₀ −Γ (2) In the above equation (2), ω ₀ and Γ> 0 are the angular frequency and the attenuation rate of the repron, respectively. The relation between k and α (dispersion relation equation) is obtained by applying the Navier-Stokes equation and the equation of continuity to the liquid surface, (1) the amplitude is sufficiently smaller than the wavelength, and (2) the motion is deep in the liquid. It is derived as follows by Lamb and Levich under the condition that there is no generation, (3) no surface shear stress, and (4) the wavelength is short and the gravitational term is negligible.

Ω ₀ ² = (σ / ρ) k ³ (3) Γ = 2 (η / ρ) k ² (4) where σ is the surface tension, ρ is the density of the liquid, η is the viscosity.

Therefore, the surface tension σ and the viscosity η can be obtained by measuring the angular frequency ω ₀ , the attenuation rate Γ, and the wave number k of the ripron and assuming that the density ρ of the liquid is known.

First, the angular frequency ω _{0 of the} ripron and the attenuation rate Γ
Scattered light is detected by the optical heterodyne method in order to obtain As shown in FIG. 2A, when a laser light is irradiated on the liquid surface 1 as the incident light 2, scattered light 4 is slightly generated around the specular reflection component 3. This is because the ripron acts as an amplitude-type diffraction grating, and the scattered light 4 undergoes a frequency shift according to the spectrum of the ripron (Brillouin scattering) and is scattered at a scattering angle corresponding to the wavelength of the ripron. If the frequency shift and the scattering angle are determined, the spectrum and wavelength of the ripron can be known. However, the scattered light 4 due to the ripron is weak and the shift amount (kHz to MHz) is small compared to the frequency of the light. Therefore, it is difficult to detect directly.

Therefore, as a method of detecting the scattered light 4, an optical heterodyne method is used, which can increase the signal intensity and enables analysis at a low frequency. The optical heterodyne method is a technique for performing frequency mixing of the scattered light 4 and a reference light 5 which is another reference light, and knowing information of the scattered light 4 from an optical beat signal generated thereby. Subscript relates to the scattered light 4 S, when the subscript associated with the reference beam 5 is R, respectively scattered light 4 of the reference beam 5 an electrical _{field, E S (t) = A} S exp {i (Ω S t + φ S)} ·· - (5) is represented by _{E R (t) = a R} exp {i (Ω R t + φ R)} ··· (6), the light intensity I in the case of causing interference thereof, I (t) = | E _S (t) + E _R (t) | ² = A _S ² + A _R ² + 2A _S A _R cos {(Ω _S −Ω _R ) t + (φ _S −φ _R )} (7) . Here, Ω is the frequency of light, φ is the phase of light, and A is the amplitude.

[0023] the optical heterodyne signal third term is vibrated at an amplitude 2A _S A _R, the angular frequency (Omega _S - [omega] _R) of the formula (7). Therefore, if light that is stronger than the scattered light 4 is used as the reference light 5, it is possible to amplify the fluctuation component of the scattered light 4.

Incidentally, the angular frequency (Ω) of the beat signal
_S−Ω_R) Is the angular frequency of the apron ω ₀Is equal to This point
Will be described. As shown in FIG. 3, the incident light 2 has an incident angle ψ
Incident on the ripron 10 propagating at the velocity v on the liquid surface 1
In this case, the frequency is shifted by the Doppler effect, and f ′ = (c−vsinψ) / c × f (8) Here, f is the frequency of the incident light 2.

The light of this frequency f 'is Brillouin scattered by the ripron 10, but now assuming that the liquid surface 1 is a light source, the frequency received by the fixed photodetector is f ″ = c / {c−vsin (ψ + θ)} × f ′ = (c−vsinψ) / {c−vsin (ψ + θ)} × f (9) where θ is the specular reflection of the incident light 2 This is the angle formed by the reference light 5 with respect to the component 3 or the angle formed by the reference light 5 ′ before entering the liquid surface with respect to the incident light 2.

The frequency F of the beat signal of the scattered light 4 having the frequency f ″ and the beat signal of the reference light 5 having the frequency f is as follows: F = | f ″ −f | = | (c−vsinψ) / ｛c−vsin (ψ + θ) {-1 | × f = | {−vsin} + vsin (ψ + θ)} / {c−vsin (ψ + θ)} | × f (10) From c≫v, λ · f = c (where λ is the wavelength of light), F = v / λ × | sinｓ−sin (ψ + θ) | (11)

On the other hand, as shown in FIG. 4, when the wavelength λ _{0 of the} ripron 10 is considered as the grating interval of the diffraction grating, when the incident light 2 is obliquely incident at the incident angle ψ, the scattered light 4 , Λ = | λ ₀ sinψ−λ ₀ sin (ψ + θ) | (12) Since the replon 10 is a wave propagating at the velocity v, λ ₀ · f ₀ = v (13) From Expressions (12) and (13), f ₀ = v / λ × | sinψ−sin (ψ + θ) | (14) is obtained. Since f ₀ (frequency of the ripron) in the equation (14) matches F (frequency of the beat signal) in the equation (11), the angular frequency (Ω _S −Ω _R ) of the beat signal is equal to the angular frequency ω _{0 of the} replon. It turns out that it is equal to.

When the above-mentioned optical heterodyne signal is Fourier-transformed and averaged over a certain number of times, a power spectrum P (ω) of the following formula of the repron 10 is obtained.

P (ω) = Γ / ｛(ω−ω ₀ ) ² + { ² } (15) This is called a Lorentz distribution, and a central angular frequency ω ₀ , as shown in FIG. 2 shows a spectrum having a half width of 2 °.

Therefore, by analyzing the spectrum of the scattered light 4 from the liquid surface 1, the angular frequency ω ₀ of the ripron and the attenuation rate の other than the wave number k in the equations (3) and (4) can be obtained. .

Next, a method of obtaining the wave number k of the replon will be described. In FIG. 3, it is considered that the photons of the incident light 2 elastically collide with the ripron 10 on the liquid surface 1. Consider the relationship between wave number and scattering angle. The incident light 2 of the wave vector K _in is incident at an incident angle 、, and this light is scattered by the replon 10 of the wave vector k at the scattering angle θ, and the wave vector K in
_It is considered that the scattered light 4 of the _sc has been reached. Here, storage of momentum in the x-axis direction along the liquid surface 1 is considered. _{Assuming that} the x-axis components of K _in and K _sc are K _in-x and K _sc-x , respectively, the respective momentums are hK _in-x , hk, h by the wave number and Planck's constant.
_{Expressed as} K _sc-x . From this, conservation of momentum is expressed as follows.

HK _in-x + hk = hK _sc-x (16) ∴K _in-x + k = K _sc-x (17) When equation (17) is solved for k, k ² = K _in-x ² -2K _in-x K _sc-x + K _sc-x ² = K _in ² sin ² ψ + K _sc ² sin ² (ψ + θ) -2K _in K _sc sinψ · sin (ψ + θ) (18) here in, because k is K _in, very small compared to the K _sc, K
_{If in} inK _sc , equation (18) becomes the following equation.

K = K_in| Sinψ−sin (ψ + θ) | (19) As can be seen from this equation, the wave number k of the
Wave number vector K of light 2 _in, Incident angle ψ, scattering angle θ
Can be

Since k = 2π / λ ₀ (20), it can be expressed as follows: λ ₀ = λ / | sinθ−sin (ψ + θ) | (21) Riplon 1 according to equation (21)
The wavelength λ ₀ (wave number k) of ₀ can be determined.

Now, an embodiment of the apparatus for measuring the two-dimensional distribution of surface tension and viscosity of a liquid according to the present invention for implementing the above-described measurement principle will be described. As shown in FIG. 1, a measuring apparatus according to the present invention includes a sample table 11 on which a liquid sample 30 opaque to measurement light such as fused silica melted in a crucible 31, 11, a wall member 12 standing vertically from the wall member 1, and the wall member 1
2 is a beam member 13 movably attached via a horizontal rail 14 provided on the top side of FIG.
And a substrate 20 movably attached to the beam member 13 in the horizontal X-axis direction in the plane of the drawing.
The optical system of the measurement system, the light source, and the photodetector are fixed on the vertical plane.

On the substrate 20, for example, YA as a light source
A G laser 21 is mounted, a mirror M1 for bending the optical path, and a mirror M2 for mounting a beam splitter prism BS in the optical path bent by the mirror M1, and bending the optical path reflected by the beam splitter prism BS. A mirror M3 whose angle can be freely adjusted in the optical path bent by the mirror M2 is mounted on the substrate 20, and forms an optical path of the incident light 2 in FIG. 2A. On the other hand, a mirror M4 whose angle can be adjusted is mounted on the substrate 20 in the optical path that has passed through the beam splitter prism BS.
The optical path of the reference light 5 ′ is formed. Further, an angle-adjustable mirror M5 that forms an optical path for taking in the reference light 5 specularly reflected on the liquid surface 1 of the liquid sample 30 and the scattered light 4 traveling in that direction is mounted on the substrate 20. A photodetector 22 such as a photomultiplier is attached in the optical path. The angle-adjustable mirrors M3, M4, and M5 are provided at the incident angle ψ of the incident light 2 with respect to the liquid surface 1 and at the liquid surface 1 with respect to the component 3 at which the incident light 2 is specularly reflected at the liquid surface 1. The angle θ formed by the reflected reference light 5 can be precisely set to a predetermined value.

Then, the substrate 20 on which the measuring optical system and the like are integrally mounted is moved along the beam member 13 in the horizontal X-axis direction by a drive system (not shown), and the incident light 2 and the reference light 5 ′ are The intersection (measurement point) P performs main scanning on the liquid surface 1 of the liquid sample 30. On the other hand, the beam member 13 is moved in the horizontal Y-axis direction along the top side of the wall member 12 in synchronization with the main scanning by a drive system (not shown), and the measurement point P moves on the liquid surface 1 of the liquid sample 30. Sub-scanning will be performed. For this purpose, the main scanning in the X-axis direction and the sub-scanning in the Y-axis direction are coordinated, and the optical heterodyne signal is detected from the photodetector 22 while the measurement point P is raster-scanned on the liquid surface 1 of the liquid sample 30. Then, the signal is taken into the personal computer 40 and subjected to a fast Fourier transform to take an average over a certain number of times, so that, for example, the coordinates of the measurement point P input from the drive system of the substrate 20 and the beam member 13 on the liquid surface 1 The power spectrum P (ω) at (x, y) is sequentially obtained, and from equation (15),
The angular frequency ω ₀ (x, y) of the repron at that position (x, y)
y) and the attenuation rate (x, y) are obtained.

On the other hand, it is predetermined wave number K _in the incident light 2, since scattering angle and ψ incident angle of the incident light 2 theta is determined from the fixed arrangement of the optical system or the like on the substrate 20, from the equation (19) , The wave number k of the ripron is obtained.

Therefore, from the equations (3) and (4), the two-dimensional distribution σ of the surface tension on the liquid surface 1 of the liquid sample 30 is obtained.
(X, y) and the two-dimensional distribution of viscosity η (x, y) are obtained.

As described above, according to the present invention, the optical system and the light source 21 constitute a measuring system on the substrate 20 which is mechanically two-dimensionally scanned in a horizontal plane on the sample stage 11 on which the sample liquid 30 is placed. The photodetector 22 is fixed and integrated, and the integrated substrate 20 is moved two-dimensionally along the liquid surface 1, so that the two-dimensional distribution of the surface tension and the viscosity at the liquid surface 1 can be rapidly increased. It can be easily measured. In addition, the configuration of the measuring device can be made simple and lightweight.

The apparatus for measuring the two-dimensional distribution of the surface tension and the viscosity of the liquid according to the present invention has been described above based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications are possible.

[0042]

As is apparent from the above description, according to the apparatus for measuring the two-dimensional distribution of the surface tension and the viscosity of a liquid according to the present invention, a light source for emitting light of a predetermined wavelength and a light of the predetermined wavelength for two minutes are provided. Beam splitting means, incident light deflecting means for directing one of the split incident lights toward the liquid surface at a predetermined incident angle, and the other split reference light at a predetermined incident angle different from the incident angle of the incident light. Reference light deflecting means for directing the liquid to the same position on the liquid surface, means for selectively inputting the reference light specularly reflected from the liquid surface and the scattered light of the incident light scattered in the direction to the light detector, and light detection And a detector are fixed on a common substrate, and the substrate is attached to two-dimensional scanning means for mechanically two-dimensionally scanning a horizontal plane on a sample stage on which a sample liquid is placed, and a photodetector. Heterodyne signal from the input to the Fourier transform means Which is configured such that,
The two-dimensional distribution measurement of the surface tension and the viscosity of the sample liquid, which has never been required or attempted, can be performed by a lightweight and simple device. The apparatus of the present invention is, for example, installed in an actual Czochralski method furnace to measure the surface tension distribution of an opaque and high-temperature melt such as molten silicon in the Czochralski method at the stage of crystal growth. And can contribute to obtaining uniform crystals.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a configuration of an embodiment of a two-dimensional distribution measuring device for surface tension and viscosity of a liquid according to the present invention.

FIG. 2 is a diagram for explaining a basic principle of the present invention.

FIG. 3 is a diagram showing various parameters for explaining a basic principle of the present invention.

FIG. 4 is a diagram showing scattered light when a ripron is used as a diffraction grating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid surface (liquid surface) 2 ... Incident light 3 ... Specular reflection component of incident light on the liquid surface 4 ... Scattered light 5 ... Reference light 5 '... Reference light before being incident on a liquid surface 10 ... Riplon 11 ... Sample Table 12 Vertical upright wall member 13 Horizontal beam member 14 Horizontal rail 20 Substrate 21 YAG laser 22 Photodetector 30 Liquid sample 31 Crucible 40 Personal computer BS Beam splitter prism M1, M2 Optical path bending mirror M3, M4, M5: Angle adjustable mirror P: Intersection (measurement point) of incident light and reference light

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F064 AA09 FF02 GG12 GG22 HH05 JJ05 JJ15 2G059 AA03 BB04 CC20 DD13 EE02 EE09 FF09 GG01 JJ05 JJ12 JJ13 JJ22 KK01 KK02 MM03

Claims (4)

[Claims] 1. A light having a predetermined wavelength is divided into two parts, one of which is incident light,
The other light is incident on the same position on the liquid surface as the reference light at different angles of incidence, and the reference light reflected specularly from the liquid surface and the scattered light of the incident light scattered in that direction interfere with each other to generate an optical heterodyne signal. Detect the frequency, determine the frequency and attenuation of the replon on the liquid surface from the power spectrum obtained by Fourier transforming the optical heterodyne signal, and calculate the incident angle of the incident light, the scattering angle of the scattered light, and the wave number of the incident light. In the apparatus for measuring the wave number of the ripron from the obtained, the surface tension and the viscosity of the liquid from the frequency and attenuation rate of the obtained ripron and the wave number of the incident light, a light source that emits light of the predetermined wavelength, Beam splitting means for splitting the light into two, incident light deflecting means for directing one of the split incident lights to the liquid surface at a predetermined incident angle, and a predetermined splitting of the other split reference light which is different from the incident angle of the incident light of Reference light deflecting means for directing the same position on the liquid surface at an incident angle, and means for selectively causing the reference light specularly reflected from the liquid surface and the scattered light of the incident light scattered in that direction to the photodetector. And a photodetector are fixed on a common substrate, and the substrate is attached to two-dimensional scanning means that mechanically two-dimensionally scans in a horizontal plane on a sample stage on which the sample liquid is placed, An apparatus for measuring a two-dimensional distribution of surface tension and viscosity of a liquid, wherein an optical heterodyne signal from the photodetector is input to a Fourier transform unit. 2. An apparatus according to claim 1, wherein said incident light deflecting means and said reference light deflecting means are adjustable in angle. 3. The two-dimensional distribution measuring apparatus according to claim 1, wherein the sample liquid is a liquid opaque to incident light. 4. The two-dimensional distribution measuring apparatus according to claim 3, wherein the sample liquid is a high-temperature melt.